Carbohydrate esters as inducers for gene expression

ABSTRACT

The invention provides novel carbohydrate esters, in particular disaccharide esters, and the methods of their preparation. These compounds find use as microbial media components for the induction of gene expression in microbial fermentation processes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional ApplicationsSer. No. 61/673,997, filed Jul. 20, 2012, and 61/746,120, filed Dec. 27,2012, the contents of which are incorporated in their entirety.

STATEMENT AS TO FEDERALLY SPONSORED RESEARCH

The U.S. government owns certain rights in the present applicationpursuant to grant number #2012-33610-19542 from the United StatesDepartment of Agriculture.

TECHNICAL FIELD

The present invention relates to chemical compounds and methods of theirpreparation for use as inducers of gene expression in cell culturing.More particularly, this invention is related to the development of lowcost and highly efficient protein inducers that significantly lower themanufacturing cost for enzyme manufacturers.

BACKGROUND OF THE INVENTION

Cheap and readily available industrial enzymes are the key driversbehind the industrial biotechnology revolution where chemicals andenergy fuels are increasingly being produced biologically usingrenewable resources. In contrast to high margin enzymes or otherproteins used for therapeutic and diagnostic purposes, industrialenzymes typically have lower margins and are manufactured in largequantities with limited downstream processing after fermentation. Forthe industrial enzyme market, the production costs are of criticalimportance to commercial success. In order to fulfill the increasingdemand for cheaper and readily available enzymes for the renewablechemicals and energy industries, there is an urgent need for moreefficient and cost-effective production processes.

Major industrial enzyme manufacturers all have significant productioncapacities devoted to fungal fermentation, in particular usingfilamentous fungi such as Aspergillus spp, Penicillium spp, Trichodermaspp., Chrysosporium lucknowense (C1) and Myceliophthora thermophila(reclassified)), to make a range of enzyme products used in the textile,detergent, food and feed, and the nascent biofuels industries (Sharma etal., World J. of Microbiol. and Biotech., 25(12):2083-2094 (2009);Visser et al., Industrial Biotech., 7(3):214-223 (2011)).

Commercial production of a protein of interest in Aspergillus andTrichoderma typically requires an inducer compound that activates thetranscriptional switch under a strong native promoter driving a gene ofinterest expressing a targeted enzyme or protein. Insoluble substratessuch as starch and cellulose are typically used in laboratory scale toinduce protein expression in Aspergillus and Trichoderma, respectively.Their implementation at industrial scale, however, is hampered by poorsubstrate consistency and materials and handling issues encountered atlarge scale such as sterilization, feeding, mixing, and viscosityissues. Consequently, highly efficient soluble inducers are morepreferred in the commercial production of enzymes and other proteins.

Maltose, isomaltose, and maltodextrins are commonly used as solubleinducers for the induction of alpha-amylase and glucoamylase enzymes inAspergillus spp. (Barton et al., J. Bacteriol., b(3):771-777 (1972)),while sophorose, cellobiose, and lactose are three effective solubleinducers widely used in the industry for enzyme production inTrichoderma spp. (Kubicek et al., Biotech. Biofuels, 2:19 (2009)).Sophorose, a beta 1, 2-disaccharide, is considered to be the mostpowerful inducer of the cellulase gene promoter in Trichoderma reesei,being 2500 times as active as cellobiose (Mandels et al., J. Bacteriol.,83(2):400-408 (1962)). These respective soluble inducers are allmetabolized by Aspergillus or Trichoderma before, during, or afterinduction. Therefore, they are not considered as gratuitous inducers,thus requiring them to be continually supplied during the fermentationin order to achieve optimum induction.

In industrial enzyme production through submerged fermentation, solubleinducers are typically supplied to the fermenter in a fed batch eitheralone or supplemented with alternative carbon sources such as glucose ina carbon-limited fashion. Due to the inducers being non-gratuitous, theinduction process, if not fully optimized, will typically causecatabolic repression that significantly lowers the productivity, alongwith unnecessary growth that significantly lowers the yield. Thus, thereexists a need in the art for a stronger, gratuitous, or nearlygratuitous inducer that decouples induction from unintended repression,growth, or other physiological functions, allowing more rigorous processoptimization to significantly improve productivity and yield than iscurrently possible. A more powerful inducer can also be easily used tosupply the induction needs of cheaper and non-inductive feedstocks aswell as to enhance the induction of conventional inducers such aslactose, cellulose, maltodextrins, or cheaper alternatives such asstarch and cellulose hydrolysates, and also in alternative productionprocesses such as solid-phase fermentations.

Because carbohydrate-based inducers are both inducers and repressors forprotein expression, methods to enhance the induction power by modifyingthe inducer to slow its uptake or metabolization are known. Hydrolysisproducts of cellobiose octaacetate, although not characterized, areknown to carry superior induction power than cellobiose (Mandels andReese, J. Bacteriol., 79(6):816-826 (1960)). Sucrose monopalmitateinduced a sucrase yield that is 80 times that of sucrose in Pullulariapullulans (Reese et al., J. Bacteriol., 100(3):1151-1154 (1969)).Similarly, acetyl cellobioses were more effective than glucose orcellobiose at inducing cellulase in Penicillium purpurogenum, withmono-O-acetyl cellobiose being the most active inducer tested (Suto etal., J. Ferment. Bioengin., 72(5):352-357 (1991)). A recent filing bythe inventor (International Application No.: WO 2013/003291) disclosed anovel class of sophorose esters derived from dilute acid treatment ofnatural sophorolipid that is at least a 30 times more powerful inducerthan sophorose itself.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the present invention provides a method for producing aprotein of interest comprising providing a fermentation host andculturing the fermentation host with a carbon source and one or morecompounds selected from the group consisting of:

where R_(a) is H or C(O)R;

R_(b) is H or C(O)R;

R_(c) is H or C(O)R;

R_(d) is H or C(O)CH₃;

R_(e) is H or C(O)CH₃;

R_(f) is H or C(O)CH₃;

R_(g) is H or C(O)CH₃; and

R is an aliphatic moiety, with the proviso that in formula (II), R_(c)is H when R_(a) is H or C(O)CH₃ and R_(b) is H or C(O)CH₃, wherein thefermentation host is cultured under conditions sufficient to produce aprotein of interest. In one embodiment, the protein of interest iscellulase or amylase. In another embodiment, the protein of interest isa homologous or heterologous protein. In a further embodiment, thehomologous or heterologous protein is an enzyme, a hormone, a growthfactor, a cytokine or an antibody. In one embodiment, the fermentationhost is capable of producing cellulase or amylase. In anotherembodiment, the fermentation host is a filamentous fungus or bacteria orother hosts selected from the genus group consisting of Trichoderma,Humicola, Pleurotus, Fusarium, Aspergillus, Streptomyces,Thermomonospora, Bacillus, Cellulomonas, Penicillium, Basidiomycete,Chrysoporium, Pestalotiopsis, Neurospora, Cephalosporium, Achlya,Podospora, Endothia, Mucor, Cochliobolus, Myceliopthora, Talaromyces,and Pyricularia. In a further embodiment, the fermentation host is thefilamentous fungus Trichoderma reesei or Aspergillus niger. In oneembodiment, the fermentation host is grown in a liquid culture or on asolid substrate without free-flowing liquid. In another embodiment, thefermentation host has a promoter operably linked to a gene encoding aprotein of interest. In a further embodiment, the promoter is acellulase gene promoter or an amylase gene promoter. In anotherembodiment, the promoter is a cbh1 promoter or a glaA promoter or anamyA promoter. In one embodiment, the carbon source is biomass. Inanother embodiment, the biomass is glucose, sucrose, fructose, glycerol,lactose, cellulose, cellulose hydrolysate, starch, starch hydrolysate,maltose, or maltodextrin.

In another aspect, the compound of formula (I), (II), (III), (IV) and(V) is isolated from a crude product mixture from either a chemical orenzymatically catalyzed trans-esterification reaction. In oneembodiment, the compounds of formula (VI) are isolated from formic acidtreatment process of natural lactonic sophorolipid. In anotherembodiment, the compounds of formula (VII) are isolated from the cultureof the yeast Candida bombicola. In another embodiment, R is an aliphaticmoiety selected from unsubstituted C₁-C₂₄ alkyl, substituted C₁-C₂₄alkyl, unsubstituted C₂-C₂₄ alkenyl, and substituted C₂-C₂₄ alkenyl. Ina further embodiment, R is an aliphatic moiety selected from C₁-C₂₄alkyl substituted with hydroxyl groups and C₂-C₂₄ alkenyl substitutedwith hydroxyl groups. In yet another embodiment, R is an aliphaticmoiety selected from C₁-C₂₄ alkyl substituted with carboxyl groups andC₂-C₂₄ alkenyl substituted with carboxyl groups. In a furtherembodiment, R is an aliphatic moiety selected from C₁-C₂₄ alkylsubstituted with aromatic groups and C₂-C₂₄ alkenyl substituted witharomatic groups. In another embodiment, the compound of formula (I),(II), (III), (IV), (V), (VI), and (VII) comprises:

where R_(d) is H or C(O)CH₃;

R_(e) is H or C(O)CH₃;

R_(f) is H or C(O)CH₃;

and R_(g) is H or C(O)CH₃.

In another aspect, the present invention provides a method for producingone or more compounds of formula (I), formula (II), formula (III),formula (IV) or formula (V) comprising providing a disaccharide; andcontacting the disaccharide with a vinyl ester in the presence of alipase enzyme in a solvent system. In one embodiment, the disaccharidecomprises lactose, sophorose, cellobiose, maltose, or isomaltose. Inanother embodiment, the lipase enzyme comprises Novozyme 435, LipozymeTL, Lipozyme RM, or Amano lipase PS. In a further embodiment, the vinylester comprises vinyl acetate, vinyl propionate, vinyl butyrate, vinylcinnamate, vinyl methacrylate, vinyl oleate, vinyl linoleate, vinylpalmitate, or vinyl stearate. In another embodiment, the solvent systemcomprises a polar solvent mixed with tert-amyl alcohol, tert-butylalcohol, tetrahydrofuran, acetone, methanol, or acetonitrile. In afurther embodiment, the polar solvent comprises dimethyl sulfoxide(DMSO), pyridine, or dimethylformamide (DMF). In another embodiment themethod further comprises heating to a temperature between 40° C. to 100°C. In yet another embodiment, the method further comprises vacuumdistillation to remove the solvent system and isolating the product ofinterest.

In another aspect, the present invention provides a method for producingone or more compounds of formula (I), formula (II), formula (III),formula (IV) or formula (V) by an acid or base catalyzedtrans-esterification reaction of an appropriate disaccharide with asuitable vinyl ester in a solvent system. In one embodiment, the base ispotassium carbonate (K₂CO₃), sodium hydroxide (NaOH), or potassiumhydroxide (KOH). In another embodiment, the acid is sulfuric acid(H₂SO₄) or hydrochloric acid (HCl). In a further embodiment, the vinylester comprises vinyl acetate, vinyl propionate, vinyl butyrate, vinylcinnamate, vinyl methacrylate, vinyl oleate, vinyl linoleate, vinylpalmitate, or vinyl stearate. In another embodiment, the solvent systemcomprises a polar solvent such as dimethyl sulfoxide (DMSO), pyridine,or dimethylformamide (DMF).

In another aspect, the present invention provides a method for producingone or more compounds of formula (VI) comprising reacting naturallactonic sophorolipid with formic acid or acetic acid undersubstantially non-aqueous conditions and partially or completelyremoving formate or acetate esters formed. In one embodiment, a secondacid catalyzes the reaction of the natural sophorolipid with formic acidor acetic acid. In another embodiment, the second acid comprisessulfuric acid (H₂SO₄) or hydrochloric acid (HCl). In a furtherembodiment, the natural sophorolipid is produced by a fermentation host.In another embodiment, the fermentation host is Candida bombicola. Inone embodiment, the substantially non-aqueous conditions comprise areaction mixture having a water content of no more than about 10%.Another embodiment further comprises the step of heating at atemperature between 40° C. to 120° C. before the step of partially orcompletely removing the formate or acetate esters formed. In a furtherembodiment, the removal of the formate esters comprises refluxing inacetic acid and methanol. In another embodiment, the removal of theacetate esters comprises treating with an acid or a base.

In another aspect, the present invention provides a method for producingone or more compounds of formula (VII) by a fermentation host. In oneembodiment, the fermentation host is Candida bombicola. In anotherembodiment, the compounds of formula (VII) and (VIIa) are isolated froma crude mixture from a culture of Candida bombicola.

In another aspect, the present invention provides a method for producingsophorose comprising reacting natural sophorosides with formic acidunder substantially non-aqueous conditions and completely removingformate esters formed, wherein a purified sophorose is obtained. In oneembodiment, the natural sophorosides are steviosides, sophorolipids, andflavonoid sophorosides. In another embodiment the step of reactingnatural sophorosides with formic acid step is catalyzed by a secondacid. In one embodiment, the second acid comprises sulfuric acid (H₂SO₄)or hydrochloric acid (HCl). In a further embodiment, the substantiallynon-aqueous conditions comprise a reaction mixture having a watercontent of no more than about 10%. In another embodiment, the methodfurther comprises the step of heating at a temperature between 40° C. to120° C. before the step of completely removing the formate esters. In afurther embodiment, the step of completely removing the formate esterscomprises treating with a base in a solvent. In one embodiment, the baseis sodium methoxide (CH₃NaO) or ammonia (NH₃) and the solvent ismethanol or ethanol.

In another aspect, the present invention provides a compound having astructure of formula (II):

wherein:

R_(a) is H or C(O)R;

R_(b) is H or C(O)R;

R_(c) is H or C(O)R; and

R is an aliphatic moiety, with the proviso that R_(c) is H when R_(a) isH or C(O)CH₃ and R_(b) is H or C(O)CH₃. In one embodiment, R is selectedfrom the group consisting of unsubstituted C₁-C₂₄ alkyl; C₁-C₂₄ alkylsubstituted with hydroxyl, carboxyl or aromatic groups; unsubstitutedC₂-C₂₄ alkenyl; and C₂-C₂₄ alkenyl substituted with hydroxyl, carboxylor aromatic groups. In another embodiment, R is an aliphatic moietyselected from unsubstituted C₁-C₂₄ alkyl, substituted C₁-C₂₄ alkyl,unsubstituted C₂-C₂₄ alkenyl, and substituted C₂-C₂₄ alkenyl. In afurther embodiment, R is an aliphatic moiety selected from C₁-C₂₄ alkylsubstituted with hydroxyl groups and C₂-C₂₄ alkenyl substituted withhydroxyl groups. In another embodiment, R is an aliphatic moietyselected from C₁-C₂₄ alkyl substituted with carboxyl groups and C₂-C₂₄alkenyl substituted with carboxyl groups. In a further embodiment, R isan aliphatic moiety selected from C₁-C₂₄ alkyl substituted with aromaticgroups and C₂-C₂₄ alkenyl substituted with aromatic groups.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 shows examples of carbohydrate esters for use as inducers forgene expression: (A) 6″ acetylated lactose monoester; (B) 6′ and 6″acetylated alpha-sophorose diester; (C) 6′ and 6″acetylated maltosediester; (D) a deacetylated or 6′ and/or 6″ acetylated alpha-sophoroseester esterified at C-4″ position with an 18-carbon monounsaturatedfatty alcohol hydroxylated at the C-17 position of the fatty alcoholchain; and (E) a deacetylated or 6′ and/or 6″ acetylated dimericsophorolipid ester. In this figure, R_(d)═H or C(O)CH₃; R_(e)═H orC(O)CH₃; R_(f)═H or C(O)CH₃; and R_(g)═H or C(O)CH₃.

FIG. 2 shows examples of two additional compounds resulting from theformic acid treatment of lactonic sophorolipid containing amonounsaturated fatty acyl moiety: (A) sophorose ester with a 17-hydroxyfatty acyl group substituted with an additional hydroxyl at 9 positionand (B) at 10 position. In this figure, R_(d)═H or C(O)CH₃; R_(e)═H orC(O)CH₃; R_(f)═H or C(O)CH₃; and R_(g)═H or C(O)CH₃.

FIG. 3 depicts a synthesis route for the preparation of carbohydrateesters: (A) preparation of lactose, cellobiose, maltose, and sophoroseesters through chemical or enzymatically catalyzed trans-esterification;and (B) preparation of sophorolipid and dimeric sophorolipid esterthrough C. bombicola fermentation and preparation of sophorose andsophorose ester through formic acid treatment of sophorolipid followedby full and partial de-esterification, respectively. In this figure,R_(a)═H or C(O)R; R_(b)═H or C(O)R; R_(c)═H or C(O)R; R_(d)═H orC(O)CH₃; R_(e)═H or C(O)CH₃; R_(f)═H or C(O)CH₃; and R_(g)═H or C(O)CH₃;and R is an aliphatic moiety.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the chemical or biological modificationof known carbohydrate inducers such as lactose, sophorose, and maltosein a cost effective manner that enhances their induction power in theproduction of industrially desirable proteins. The induction power oflactose, sophorose, and maltose is enhanced by several folds bymodification to disaccharide esters, in particular as solublemonoesters, diesters, and triesters. Significantly improved yields ofcellulase, amylase or other proteins under the control of a suitablepromoter can be induced at higher yields than is currently possible. Thepresent invention has the potential to significantly impact currentenzyme production economics by improving both productivity andoperations logistic in the manufacturing plant.

The present invention also relates to a more effective method to producenovel and highly inductive sophorose esters from natural lactonicsophorolipid and the use of a novel, sophorolipid dimer ester compoundas a highly potent inducer. Due to the ease of preparation of this newclass of compounds, ready-to-use and industrially applicable inducerscan be produced, which are also highly efficient and cost-effective.Furthermore, a more effective method of producing sophorose from naturalsophorosides such as stevioside and sophorolipid is also described.

Carbohydrate Esters

Lactose, sophorose, cellobiose, maltose, or isomaltose monoester ordiester compounds are produced by a trans-esterification reaction ofunmodified disaccharide and a vinyl ester according to the method of thepresent invention. FIGS. 1A through 1C depict three exemplarydisaccharide monoacetates or diacetates that can be produced chemicallyor enzymatically from the trans-esterification reaction of adisaccharide and a vinyl acetate according to the method of theinvention. FIG. 1A shows a lactose monoacetate ester, while FIG. 1Bdepicts a sophorose diacetate ester. FIG. 1C shows a maltose diacetateester. All three compounds are esterified at the 6′ and/or 6 position.

In another embodiment, sophorose esters are produced by the reaction offormic acid or acetic acid with natural lactonic sophorolipids undernon-aqueous conditions resulting in a formyl- or acetyl-protected andC-1′ ring-opened sophorolipid. This is followed by partial or completecleavage of the formate or acetate esters from the treated sophorolipid.Other side products, such as unmodified sophorolipids and higher esters(esters with DS>3), may also be present. FIG. 1D depicts a deacetylatedor 6′ and/or 6″ acetylated alpha-sophorose ester esterified at C-4″position with an 18-carbon monounsaturated fatty alcohol hydroxylated atthe C-17 position of the fatty alcohol chain. The compound was producedby formic acid reaction of natural diacetylated lactonic sophorolipid(obtained from the culture of C. bombicola) catalyzed by sulfuric acidfollowed by cleavage of formate ester from the treated parent compoundby heating or refluxing the substrate in an acetic acid and methanolmixture. Sulfuric acid is an inexpensive and readily available catalyst.Formic acid can also participate in an addition reaction with lactonicsophorolipids that contain unsaturation on their fatty acyl moiety andmay result in the formation of a hydroxyl group on the unsaturatedpositions upon the cleavage of formate ester. Two exemplary products areprovided in FIG. 2 that result from the formic acid treatment oflactonic sophorolipid containing an 18-carbon fatty acyl moietymonounsaturated at 9 position. FIG. 2A and FIG. 2B depict a sophorolipidester with a 17-hydroxy fatty acid substituted with an additionalhydroxyl at 9-position and 10-position, respectively.

In another aspect, a sophorose dimer is produced by the yeast C.bombicola using the method of the invention. The compound may beisolated from the crude culture of C. bombicola where other sideproducts may consist of natural acetylated lactonic or acidicsophorolipid. FIG. 1E depicts a deacetylated or 6′ and/or 6″ acetylatedsophorolipid dimer ester esterified at C-4″ position with an 18-carbonmonounsaturated fatty chain. The compound is produced by fermentation ofC. bombicola using glucose and canola oil as feedstock.

The lactose, sophorose, cellobiose, maltose, isomaltose esters,sophorose ester (obtained from formic acid treatment of natural lactonicsophorolipid), and the sophorolipid dimer produced by the method of theinvention have the structures depicted by formula (I), (II), (III),(IV), (V), (VI), and (VII), respectively:

where R_(a) is H or C(O)R;

R_(b) is H or C(O)R;

R_(c) is H or C(O)R;

R_(d) is H or C(O)CH₃;

R_(e) is H or C(O)CH₃;

R_(f) is H or C(O)CH₃;

R_(g) is H or C(O)CH₃; and

R is an aliphatic moiety, with the proviso that in formula (II), R_(c)is H when R_(a) is H or C(O)CH₃ and R_(b) is H or C(O)CH₃.

In some embodiments, R is an aliphatic moiety selected fromunsubstituted C₁-C₂₄ alkyl, substituted C₁-C₂₄ alkyl, unsubstitutedC₂-C₂₄ alkenyl, and substituted C₂-C₂₄ alkenyl.

In other embodiments, R is an aliphatic moiety selected from C₁-C₂₄alkyl substituted with hydroxyl groups and C₂-C₂₄ alkenyl substitutedwith hydroxyl groups.

In further embodiments, R is an aliphatic moiety selected from C₁-C₂₄alkyl substituted with carboxyl groups and C₂-C₂₄ alkenyl substitutedwith carboxyl groups.

In certain embodiments, R is an aliphatic moiety selected from C₁-C₂₄alkyl substituted with aromatic groups and C₂-C₂₄ alkenyl substitutedwith aromatic groups.

In some embodiments, the esters produced by the method of the inventionhave the structures depicted by compounds of formula (Ia), (IIa),(IIIa), (IVa), (Va), (VIa), or (VIIa):

where R_(d) is H or C(O)CH₃; R_(e) is H or C(O)CH₃; R_(f) is H orC(O)CH₃; and R_(g) is H or C(O)CH₃.

In a further embodiment, the sophorose ester is a novel compound havinga structure of formula (II):

wherein:

R_(a) is H or C(O)R;

R_(b) is H or C(O)R;

R_(c) is H or C(O)R; and

R is an aliphatic moiety, with the proviso that R_(c) is H when R_(a) isH or C(O)CH₃ and R_(b) is H or C(O)CH₃.

As used herein, an “aliphatic” moiety is a non-aromatic carbon moiety.In some embodiments, an aliphatic moiety may include a linear, branchedor cyclic carbon moiety. In certain embodiments, an aliphatic moiety mayinclude a saturated or unsaturated moiety, including both monovalent andbivalent moieties. In some embodiments, the aliphatic moiety is analiphatic alkyl, an aliphatic alkenyl, an aliphatic alkynyl, analiphatic cycloalkyl, an aliphatic cycloalkenyl, an aliphaticcycloalkynyl, or any bivalent radicals thereof.

“Alkyl” includes saturated linear or branched hydrocarbon structures,and combinations of these, which contain only carbon and hydrogen atomswhen unsubstituted. In some embodiments, alkyl groups have one totwenty-four carbon atoms (i.e., C₁-C₂₄ alkyl), five to twenty-fourcarbon atoms (i.e., C₅-C₂₄ alkyl), or fifteen to eighteen carbon atoms(i.e., C₁₅-C₁₈ alkyl). When an alkyl residue having a specific number ofcarbon atoms is named, all geometric isomers having that number ofcarbon atoms may be encompassed. For example, “butyl” may, in someembodiments, include n-butyl, sec-butyl, iso-butyl, and tert-butyl;“propyl” may, in some embodiments, include n-propyl and iso-propyl. Insome embodiments, the alkyl group may be substituted. In one embodiment,substituted alkyl groups may have a hydroxyl substituent. Alkyl groupssubstituted with hydroxyl may include, for example, —(CH₂)₂OH and—(CH₂)₄OH. In another embodiment, substituted alkyl groups may have acarboxyl substituent. Alkyl groups substituted with carboxyl mayinclude, for example, —(CH₂)₂COOH. In another embodiment, substitutedalkyl groups may have an aromatic substituent. Alkyl groups substitutedwith aromatic may include, for example, —CH₂(phenyl).

“Cycloalkyl” refers to a cyclic alkyl group, and can have one ring(e.g., cyclohexyl) or multiple rings (e.g., adamantyl).

“Alkylene” refers to the same residues as alkyl, but having bivalency.Examples of alkylene include methylene (—CH₂—), ethylene (—CH₂CH₂—),propylene (—CH₂CH₂CH₂—), butylene (—CH₂CH₂CH₂CH₂—), as well as longerchains including —(CH₂)₁₇—.

“Alkenyl” refers to an unsaturated hydrocarbon group having at least onesite of olefinic unsaturation (i.e., having at least one moiety of theformula —C═C—). When the alkenyl has one site of olefinic unsaturation,the alkenyl is monounsaturated. When the alkenyl has two or more sitesof olefinic unsaturation, the alkenyl is polyunsaturated. In someembodiments, alkenyl groups have two to twenty-four carbon atoms (i.e.,C₂-C₂₄ alkenyl), five to twenty-four carbon atoms (i.e., C₅-C₂₄alkenyl), or fifteen to eighteen carbon atoms (i.e., C₁₅-C₁₈ alkenyl).Alkenyl groups may include, for example, —CH₂—CH═CH—CH₃ and—(CH₂)₇—CH═CH—(CH₂)₇—CH₃. In some embodiments, the alkenyl group may besubstituted. In one embodiment, substituted alkenyl groups may have ahydroxyl substituent. Alkenyl groups substituted with hydroxyl mayinclude, for example, —(CH₂)₂OH and —(CH₂)₄OH. In another embodiment,substituted alkenyl groups may have a carboxyl substituent. Alkenylgroups substituted with carboxyl may include, for example, —(CH₂)₂COOH.In another embodiment, substituted alkenyl groups may have an aromaticsubstituent. Alkenyl groups substituted with aromatic may include, forexample, —CH₂(phenyl).

“Cycloalkenyl” refers to a cyclic alkenyl group and can have one ring(e.g., cyclohexenyl, —CH₂—CH₂-cyclohexenyl), or multiple rings (e.g.,norbornenyl).

“Alkenylene” refers to the same residues as alkenyl, but havingbivalency. Examples of alkenylene include ethylene (—CH═CH—), propylene(—CH₂—CH═CH—), butylene (—CH₂—CH═CH—CH₂—), as well as longer chainsincluding —(CH₂)₇—CH═CH—(CH₂)₈— and —(CH₂)₇—CH═CH—(CH₂)₆—CH═CH—.

Unless otherwise specified, the carbohydrate esters of the presentinvention depicted by structures with formula (I) through (VII) and (la)through (VIIa) have the following glycosidic linkages: formula (I),(Ia), lactose (gal(beta 1, 4)glc); formula (II), (IIa), sophorose(glc(beta 1, 2)glc); formula (III), (IIIa), cellobiose (glc(beta 1,4)glc); formula (IV), (IVa), maltose (glc(alpha 1, 4)glc); formula (V),(Va), isomaltose (glc(alpha 1, 6)glc); formula (VI), (VIa), sophorose(glc(beta 1, 2)glc); and formula (VII), (VIIa), sophorose (glc(beta 1,2)glc).

Uses of the Carbohydrate Esters

One or more carbohydrate esters produced by the methods describedherein, or any compositions thereof, can be used as inducers that causecells to produce large amounts of enzymes or other substances than theywould otherwise produce if the inducer were absent. Isolated andpurified carbohydrate esters produced by the present methods may be usedas inducers or the crude reaction mixture containing the carbohydrateesters may be used as an inducer without further purification.

In one aspect, one or more of the carbohydrate esters produced bymethods of the invention described herein, or any compositions thereof,can be used for inducing protein production (e.g., cellulase or amylaseproduction) in fermentation host organisms capable of producingcellulase or amylase in a liquid culture containing an appropriatecarbon source. For example, in certain embodiments, one or morecarbohydrate esters with a structure of formula (I) through (VII), orany compositions thereof, can be used to induce protein production.Examples of such organisms include filamentous fungi, which have theability to metabolize cellulose or starch by producing cellulases oramylase that can hydrolyze the beta-(1,4)-linked glycosidic bonds ofcellulose or alpha-(1,4)-linked glycosidic bonds of starch to produceglucose.

Suitable filamentous fungi may include all filamentous forms of thesubdivision Eumycotina. (See, Alexopoulos, C. J. (1962), IntroductoryMycology, Wiley, New York). These fungi are usually characterized by avegetative mycelium with a cell wall composed of chitin, cellulose, andother complex polysaccharides. Suitable species of filamentous fungi orbacteria or other hosts for use with the carbohydrate ester inducers ofthe present invention include, for example, hosts selected from thefollowing genera: Trichoderma, Humicola, Pleurotus, Fusarium,Aspergillus, Streptomyces, Thermomonospora, Bacillus, Cellulomonas,Penicillium, Basidiomycete, Chrysoporium, Pestalotiopsis, Neurospora,Cephalosporium, Achlya, Podospora, Endothia, Mucor, Cochliobolus,Myceliopthora, Talaromyces and Pyricularia. Specific hosts may include,for example, Trichoderma reesei (QM 9414, MCG 77, MCG 80, Rut-C30,CL-847, VTT-D, SVG, and RL-P37) (see Esterbauer et al., BioresourceTech., 36(1):51-65, (1991)), Aspergillus niger, Aspergillus oryzae,Bacillus subtilis, Penicillium decumbens, Penicillium funiculosum,Penicillium purpurogenum, Chrysosporium lucknowense, Myceliopthorathermophila, and Talaromyces emersonii.

In some embodiments, one or more of the carbohydrate esters produced bythe methods of the present invention, or any compositions thereof, areused to induce protein production (e.g., cellulase or amylaseproduction) in a host cell that is a member of the species ofTrichoderma, Penicillium, Chrysosporium, Humicola, Pleurotus, Fusarium,Aspergillus, Streptomyces, Thermomonospora, Myceliopthora, Talaromyces,Bacillus or Cellulomonas. In certain embodiments, one or morecarbohydrate esters, or any compositions thereof, are used to induceprotein production (e.g., cellulase or amylase production) in a hostcell that is a member of the species of Trichoderma or Aspergillus. Inone embodiment, one or more carbohydrate esters, or any compositionsthereof, are used to induce protein production in Trichoderma reesei,Trichoderma viride, Aspergillus niger, or Aspergillus oryzae. The term“Trichoderma” refers to any fungal genus previously or currentlyclassified as Trichoderma. In certain embodiments, the carbohydrateester is one or more esters with a structure of formula ((I) through(VII), or preferably, structures of formula (Ia) through (VIIa).

For industrial enzyme production, conventional inducers such as lactose,cellobiose, cellulose, cellulose hydrolysates, starch hydrolysate, andsophorose from glucose reversion are typically used to induce proteinexpression in Trichoderma reesei, while maltose, maltodextrins, starch,and starch hydrolysates are the inducers of choice for Aspergillus spp.In some case, these inducers may not perform optimally due to aninsufficient amount or unintended repression by impurities ormetabolites. Supplementing conventional inducers with the inducersdisclosed herein may increase protein expression over that achievablewith conventional inducers alone. Therefore, the use of the inducers ofthe invention may be useful either alone or in combination with eachother or with conventional inducers.

In one embodiment, induction of Trichoderma with lactose is augmented bythe addition of the sophorose esters with structure shown in FIG. 1D andFIGS. 2A and 2B. In another embodiment, induction of Trichoderma with aglucose reversion mixture containing sophorose is augmented by theaddition of the sophorose esters with structure shown in FIG. 1D andFIGS. 2A and 2B. In yet another embodiment, induction of Trichodermawith a biomass hydrolysate (e.g., cellulose, starch) is augmented by theaddition of the sophorose esters with structure shown in FIG. 1D andFIGS. 2A and 2B. In a further embodiment, induction of Aspergillusprotein expression with maltose or maltodextrins is enhanced bysupplementation of the inducer mixture with the maltose ester(s) withstructures depicted by formula IV and FIG. 1C.

In another embodiment, sophorose esters with structures of formula II,VI, and VII may be used to induce enhanced protein production in solidphase fermentation. Production of enzymes and other protein productsusing solid phase fermentation relies on the growth of microbes (inparticular, filamentous fungi) on moist solid substrates withoutfree-flowing liquid. In contrast to liquid-submerged fermentation, solidphase fermentation in some situations can offer significant advantagesin both performance and production cost. Suitable solid substratesinclude readily available and inexpensive carbon sources based onagriculture residues such as wheat bran or corn cobs, or mixturesthereof. Suitable filamentous fungi for use in this embodiment have beendescribed above and include Trichoderma reesei and Aspergillus niger.

The solid substrates are moistened with an appropriate nutrient mediumto reach a starting moisture content of 40%, 50%, 60%, or 70% to allowthe fungi to grow on the substrate. Prior to use, these solid substratesmight be activated by pretreatment with steam and chemicals known tothose skilled in the art. Crude or purified sophorose ester is mixedinto the solid substrate and fermentation is initiated by inoculatingthe mixture with an appropriately prepared culture of a suitablefilamentous fungi. The resulting product, for example, an enzyme such ascellulase is then isolated from the mixture by methods known in the art.Typical isolation involves washing the solid state fermentation mediawith a liquid. In some cases, the solid substrate might be pressedand/or a detergent might be added to the washing liquid to improveefficiency. In some applications (e.g., animal feed), the enzymes arenot isolated and are used as produced together with the solid substrate.

It should also be understood that the carbohydrate esters describedherein, or any compositions thereof, may be used with geneticallyengineered host cells. To produce proteins with recombinant DNAtechnology, a DNA construct that includes the nucleic acid encoding theamino acid sequence of the designated protein can be constructed andtransferred into, for example, a T. reesei, Aspergillus niger, orAspergillus oryzae host cell. The vector may be any vector known in theart which, when introduced into the host cell, can be integrated intothe host cell genome and can be replicated. The nucleic acid encodingthe protein can be operably linked to a suitable promoter, which showstranscriptional activity in a Trichoderma or Aspergillus host cell.Suitable promoters may include, for example, cellobiohydrolase 1 (cbh1),endoglucanase, xylanase, glucoamylase A (glaA), and Taka-amylase (amyA).In one exemplary embodiment, the carbohydrate esters described hereinwith a structure of formula (I), (II), (III), (VI), (VII), or anycompositions thereof, may be a powerful inducer of the cbh1 promoter inTrichoderma, which may increase cellulase production by several foldscompared to other known cellulase inducers. In another exemplaryembodiment, the carbohydrate esters described herein with structure offormula (IV), or (V), or any compositions thereof, may be a powerfulinducer of the glaA or amyA promoter in Aspergillus, which may increaseamylase production by several folds compared to other known amylaseinducers.

It should be understood, however, that the carbohydrate esters describedherein, or any compositions thereof, may induce production of anyprotein that may be under the control of a native or engineeredpromoter, such as cbh1 or glaA. The promoter may be derived from genesencoding proteins that may be either homologous or heterologous to thehost cell. One of skill in the art would recognize that a promoter canbe engineered to enhance its function and the applicability of this newinducer should not be constrained by its alteration. Homologous orheterologous protein expression under this promoter may be routinelycarried out using recombinant molecular biology techniques known in theart, which may rely on successful recombination of genes encoding theprotein of interest. Examples of homologous and heterologous proteins ofinterest include, for example, enzymes, hormones, growth factors,cytokines, vaccines, antibodies, and polypeptides. In some embodiments,the carbohydrate esters described herein may induce production ofenzymes including, for example, cellulases, amylases, proteases,xylanases, lipases, esterases, phytases, pectinases, catalases,pullulanases, laccases, oxidases, glucose isomerases, lyases, acylases,and transferases.

Fermentation procedures for production of proteins are generally knownto one of skill in the art. Generally, cells are cultured in a mediumcontaining physiological salts and nutrients. (See, e.g., Pourquie, J.et al., Biochemistry and Genetics of Cellulose Degradation, Aubert, J.P. et al., eds., Academic Press, pp. 71-86, 1988; and Ilmen, M. et al.,Appl. Environ. Microbiol., 63:1298-1306 (1997). For example, Trichodermaand Aspergillus cells may be cultured in the medium as described byEngland et al. (U.S. Published Patent Application No. 2010/0009408) andby Barton et al. (J. Bacteriol., 111(3):771-777 (1972), respectively.Culture-conditions (e.g., temperature, pH, duration) are also generallyknown in the art. For example, cultures may be incubated atapproximately 28° C. in appropriate medium in shake cultures orfermenters until desired levels of cellulase expression are achieved.After fungal growth has been established, the cells are exposed toconditions effective to cause or permit the expression of the protein.An appropriate carbon source is also provided in the culture medium.Examples of appropriate carbon source biomass include, but are notlimited to, glucose, sucrose, fructose, glycerol, lactose, cellulose,cellulose hydrolysate, starch, starch hydroylsate, maltose, ormaltodextrin.

One or more of the carbohydrate esters described herein, or anycompositions thereof, may be added to the medium at a concentrationeffective to induce protein production (e.g., cellulase or amylaseproduction). The esters may also be added to the medium in an insolubleor soluble form. In certain embodiments, the carbohydrate esters can bereconstituted in water or one or more solvents (e.g., ethanol, ordimethyl sulfoxide) prior to the introduction into the fermentationculture as a media component or as an inducing feed. Solubilizing theinducers allows for their use as a concentrated feed for proteinproduction in an industrial fed-batch fermentation process. Further, itshould be understood that the carbohydrate ester inducers may be used ina batch, fed-batch, or a continuous fermentation process.

The use of one or more of the carbohydrate esters described herein hasbeen found to surprisingly increase cellulase or amylase production byseveral folds compared to unmodified starting material such as lactose,sophorose, maltose, or natural sophorolipids. In certain embodiments,the use of one or more of carbohydrate esters, or any compositionsthereof, can increase cellulase production in a Trichoderma host (e.g.,T. reesei) or amylase production in Aspergillus host (e.g., Aspergillusniger) by at least three folds, by at least four folds, at least fivefolds, at least ten-fold, at least twenty-fold, or at least thirty-fold,greater than an unmodified lactose or sophorose. In certain embodiments,the carbohydrate esters are one or more esters with a structure offormula (I) through (VII), or preferably, with a structure of formula(Ia) through (VIIa).

While the carbohydrate esters produced by methods of the presentinvention may be used to induce protein expression directly as a crudereaction mixture containing other side products, it should also beunderstood that the active carbohydrate ester components of the crudemixture can be individually separated or isolated, and optionallyfurther purified. For example, in some embodiments, one or more esterswith a structure of formula (I) through (VII), or preferably, with astructure of formula (Ia) through (VIIa), may be isolated for use inprotein production. In some embodiments, the use of purified lactosemonoester or sophorose diester isolated from the crude ester mixture mayresult in at least a one-fold, at least a two-fold, or at least athree-fold increase in cellulase production in Trichoderma compared tothe use of an unpurified crude mixture. It should be understood that theunmodified lactose or sophorose is the one from which the lactose andsophorose esters were prepared.

The embodiments in the specification are selected to best explain theprinciples of the invention and its practical use under the describedconditions that might not be optimized. One of skill in the art wouldrecognize the induction power of these novel inducers may be enhanced byvariations in process conditions and by the alterations made to theproduction host. The applicability of this invention should not beconstrained by these variations.

Method of Preparing Carbohydrate Esters

Provided herein are methods of producing lactose, sophorose, cellobiose,maltose, and isomaltose esters by enzymatic or chemically catalyzedtrans-esterification of unmodified disaccharides with a vinyl ester.Several methods are currently known in the art for esterifyingcarbohydrates including, for example, chemical or enzymatic synthesis ofsucrose esters (Polat and Linhardt, J. Surfact. Deterg., 4(4):415-421(2001)), enzymatic synthesis of a maltose monolaurate ester (Plou etal., J. Biotech., 96:55-66 (2002)) and a lactose monolaurate ester (U.S.Patent Application Publication No. 2011/0257108), and chemical synthesisof a maltose monostearate (Allen and Tao, J. Surfact. Deterg.,5(3):245-255 (2002)).

One or more compounds of formula (I) through (V) are prepared by: a)providing a disaccharide such as lactose, sophorose, cellobiose,maltose, or isomaltose, preferably dry and preferably in high purity;and b) contacting the disaccharide with a vinyl ester and an enzyme orchemical catalyst in a suitable solvent system to produce thecomposition. In some embodiments, the reaction mixture is heated to atemperature of 40° C. to 100° C. In other embodiments, the acidhydrolysis may be performed at a temperature of at least 40° C., atleast 50° C., at least 60° C., at least 70° C., at least 80° C., atleast 90° C., or at least 100° C. In yet another embodiment, the methodfor producing a composition that includes one or more compounds offormula (I) through (V), further includes vacuum distillation to removethe solvent; and isolating the product of interest from the composition.

Vinyl esters may be fatty acid vinyl esters or aromatic vinyl esters.Suitable fatty acid vinyl esters include vinyl acetate, vinylpropionate, vinyl butyrate, vinyl methacrylate, vinyl oleate, vinyllinoleate, vinyl palmitate, and vinyl stearate. Examples of aromaticvinyl esters include vinyl cinnamate and vinyl caffiate.

Suitable lipase enzymes for use in the method of the present inventioninclude Novozyme 435 (immobilized Candida antarctica lipase B),Lipozyme® TL, Lipozyme® RM, and Amano lipase PS.

In some embodiments, the enzyme catalyst can be replaced with a chemicalcatalyst (e.g., potassium carbonate (K₂CO₃), sodium hydroxide (NaOH),sulfuric acid (H₂SO₄), and hydrochloric acid (HCl)) and the vinyl estercan be replaced with acyl chlorides (e.g., acetyl chloride or palmitoylchloride).

Suitable solvents include dimethyl sulfoxide (DMSO), pyridine,dimethylformamide (DMF), methyl ethyl ketone, isobutanol, tert-amylalcohol, tert-butyl alcohol, tetrahydrofuran, acetone, or mixturesthereof.

In one aspect, the methods described herein involve enzymatically orchemically modifying disaccharides by trans-esterification reaction witha vinyl ester. These modified disaccharide esters are highly inductiveto protein production (e.g., cellulase or amylase production) infilamentous fungi host cells (e.g., Trichoderma or Aspergillus),exceeding the inductive ability of unmodified starting materials byseveral folds.

The methods described herein typically yield a crude mixture consistingof active carbohydrate ester as component(s). Any separation techniquesknown in the art may be employed to isolate the active esters, forexample, vacuum distillation, precipitation, crystallization, solventextraction, or column chromatography.

One skilled in the art will recognize many variations can be madefollowing the spirit of the invention. In certain embodiments, otherdisaccharides and soluble polysaccharides may be modified into potentinducers using the same principles disclosed in this invention. Examplesof other disaccharides include sucrose, trehalose, gentiobiose,laminaribiose, and xylobiose. Examples of polysaccharides includecellodextrins and maltodextrins.

Provided herein are also methods for producing novel and highlyinductive sophorose esters with a structure of formula of (VI) by formicacid or acetic acid reaction with natural lactonic sophorolipid undersubstantially non-aqueous conditions followed partial or completecleavage of formate or acetate esters from the formyl- oracetyl-protected and C-1′ lactone ring-opened sophorolipid. In order toobtain a compound with a structure of formula of (VI), a naturallactonic sophorolipid needs to be ring-opened through selective cleavageof the ether-like linkage at the C-1′ (the anomeric carbon) position,followed by regeneration of the hydroxyl group of the hydroxy fattyacid, which remains linked by an ester bond to C-4″ (as shown in FIG.1D). Previously described methods for this transformation are limited bythe low yields obtained. The inventor disclosed the use of 0.1Nhydrochloric acid with natural sophorolipid under aqueous conditions toproduce these compounds (International application no.: WO 2013/003291).The present invention comprises a high yield method involving thereaction of formic or acetic acid with natural lactonic sophorolipidcarried out under non-aqueous conditions. This new method promotescleavage of the ether-like linkage (C-1′) in preference to the esterlinkage (C-4″) of the natural lactonic sophorolipid, thus resulting in ahigh yield. Unintended formate and acetate esters may be formed with theopen hydroxyls during the formic acid or acetic acid treatment ofsophorolipid, which require cleavage in order to yield compoundsdescribed by formula (VI).

The formic acid or acetic acid reactions may be catalyzed by anotheracid. Examples of suitable acid catalyst include, for example, sulfuricacid (H₂SO₄) or hydrochloric acid (HCl), or mixtures of acid catalysts,at a concentration (wt %) between about 0.05% to about 1%. Appropriateconcentrations include 0.05%, 0.10%, 0.15%, 0.20%, 0.30%, 0.50%, 0.75%,and 1%. The natural lactonic sophorolipid may be produced by afermentation host, including, but not limited to, C. bombicola.Substantially non-aqueous conditions may comprise a water content of nomore than about 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less than1%, by weight.

In some embodiments, the acid treatment is performed at elevatedtemperatures. The formic acid and acetic acid treatment may becharacterized as a formolysis and an acetolysis reaction, respectively.In certain embodiments, the formolysis or acetolysis may be performed ata temperature of at least 40° C. In other embodiments, the formolysis oracetolysis may be performed at a temperature of at least 80° C., atleast 90° C., at least 100° C., at least 110° C. or at least 120° C. Inother embodiments, the formolysis or acetolysis may be performed at atemperature between 40° C. and 120° C., or between 100° C. and 120° C.The natural sophorolipid mixture can be contacted with the acid atelevated temperatures for a range of time, e.g., from minutes to hours.

In one embodiment, the cleavage of formate ester from the lactonering-opened sophorolipid involves heating or refluxing the startingmaterial in an acetic acid and methanol mixture. For example, the ratioof acetic acid to methanol may be 3:2 (v/v). In another embodiment, thecleavage of acetate esters involves treating the starting material withan acid, for example, HCl, or a base, for example, ammonia, or anenzyme, for example, esterase. The cleavage of the formate or the aceticester from the treated sophorolipid may be partial. Migration of fattyand acetyl acyl groups may occur during the cleavage. Further, thelactonic sophorolipid containing single or multiple unsaturation on itsfatty acid acyl moiety may participate in an addition reaction withformic acid at the unsaturated positions and the cleavage of formateesters may result in the formation of the hydroxyl group on theunsaturated positions in cases where the sophorose ester contains monoor polyunsaturated fatty acid moieties, for example, in compounds ofdescribed in FIG. 2. One of skill in the art would recognize that apartial cleavage of formate and acetate ester, acyl migrations, andhydroxylation of unsaturation may result in new compounds that may beequal to or more inductive than the compounds with structures depictedby (VI). The applicability of this method is not be constrained by thisvariation.

In another embodiment, the natural lactonic sophorolipid may be firstpretreated with formic anhydride or acetic anhydride to yield a compoundthat is protected by formic and/or acetic esters on all open hydroxyls.This is then followed by the formic and acetic acid treatment toselectively cleave the sophorolipid lactone ring at the C-1′ anomericposition and followed by the partial or complete cleavage of formic andacetic ester from the hydroxyls. One of skill in the art would recognizethis pretreatment may result in a significant increase in yield with animproved selectivity at the C-1′ anomeric position.

In yet another embodiment, the natural laconic sophorolipid may be firstpretreated with a hydrogenation reaction to remove potentialunsaturations on its fatty acyl group (e.g., monounsaturated 17-hydroxyoleic acid, diunsaturated 17-dihydroxy linoleic acid). One of skill inthe art would recognize that this pretreatment may result in asignificant reduction in side products being produced, with the finalproduct primarily consisting of a sophorose ester with a saturated fattyacyl group. A more convenient work up may also result from thehydrogenation pretreatment.

Provided herein is also a method for using sophorolipid dimer describedby formula (VII) as a highly potent inducer. This compound was recentlydescribed by Price et al. (Carbohyd. Res., 348:33-41 (2012), althoughPrice et al. did not recognize its potential in gene induction. Incontrast to other known natural sophorolipids (e.g. acetylated anddeacylated lactonic or acidic sophorolipids), even if the dimericsophorolipid exists in trace amounts, it is surprisingly inductive togene expression in Trichoderma, as described herein. Suitablefermentation hosts for the sophorolipid dimer include, for example, C.bombicola. Examples of an appropriate feedstock for this fermentationmethod comprises glucose and a vegetable oil, including, but not limitedto, canola, soybean, corn, or palm oil. In certain embodiments,compounds of formula (VII) may be isolated as a crude mixture from theculture of Candida bombicola, and still possess surprisingly stronginductive effects.

Also provided herein is a method of producing sophorose by reactingformic acid with natural sophorosides under non-aqueous conditions,followed by complete cleavage of unwanted formate esters. Several lowyield methods are currently known in the art that include directsynthesis (Coxon and Fletcher, J. Org. Chem., 26(8):2892-2894 (1961)),acetic acid and hydrobromic acid reaction with stevioside octacacetatefollowed by deacetylation (Vis and Fletcher, J. Am. Chem. Soc.,78:4709-4710 (1956)), and a dilute hydrochloric acid treatment ofstevioside followed by purification (Kusakabe et al., Agric. Biol.Chem., 51 (8):2255-2256 (1987)).

The present invention describes a simple method of using formic acidreacting with natural sophorosides under non-aqueous conditions followedby cleavage of unwanted formate ester that gives an improved yield ofsophorose. In one aspect, a sophoroside is any compound that consists ofsophorose as one of its component. Examples of sophorosides includestevioside, sophorolipids and flavonoid sophorosides. In one embodiment,the formic acid reactions may be catalyzed by another acid. Examples ofsuitable acid catalyst include sulfuric acid (H₂SO₄) and hydrochloricacid (HCl), or mixtures of acid catalysts, at a concentration (wt %)between about 0.05% to about 1%. Appropriate concentrations include0.05%, 0.10%, 0.15%, 0.20%, 0.30%, 0.50%, 0.75%, and 1%.

In one embodiment, the sophoroside is a sophorolipid is produced from afermentation host, including, but not limited to, C. bombicola. Thesubstantially non-aqueous conditions may comprise a water content of nomore than about 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less than1%, by weight.

In some embodiments, the formic acid treatment is performed at elevatedtemperatures. In certain embodiments, the formic acid acid formolysismay be performed at a temperature of at least 40° C. In otherembodiments, the formolysis may be performed at a temperature of atleast 80° C., at least 90° C., at least 100° C., at least 110° C. or atleast 120° C. In other embodiments, the formolysis may be performed at atemperature between 40° C. and 120° C., or between 100° C. and 120° C.The natural sophorolipid mixture can be contacted with the formic acidat elevated temperatures for a range of time, e.g., from minutes tohours.

In one embodiment, the cleavage of formate esters from the treatedsophoroside involves treating the reaction mixture with a base in asolvent. Examples of suitable base include, but are not limited to,sodium methoxide (CH₃NaO) and ammonia (NH₃). Examples of suitablesolvents include, but are not limited to, methanol, ethanol, and1-propanol.

In another embodiment, the sophorosides may be first pretreated withformic anhydride or acetic anhydride to yield a compound that isprotected by formic and/or acetic esters on all open hydroxyls. Thispretreatment is then followed by the formic acid treatment toselectively cleave the sophorosides at the C-1′ anomeric position,followed by complete cleavage of formic and acetic ester from thehydroxyls. One of skill in the art would recognize this pretreatment mayresult in a significant increase in yield of sophorose due to animproved selectivity at the C-1′ anomeric position.

In yet another embodiment, the formic acid treatment of a sophorosidebased on natural lactonic and/or acidic sophorolipid may be carried outfirst after a hydrogenation reaction to remove potential unsaturationson its fatty acyl group. One of skill in the art would recognize thispretreatment may result in a significant reduction in side productsbeing produced and a more convenient work up for sophorose is expectedas a result of the hydrogenation pretreatment of the sophorolipids.

Sophorose may be isolated and purified from the final reaction mixturethrough methods known in the art. Suitable purification methods include,for example, chromatography, adsorption, extraction, precipitation,re-precipitation, crystallization, and recrystallization.

Method of Preparing Natural Lactonic Sophorolipid and DimericSophorolipid

The afore-mentioned natural lactonic sophorolipid mixture andsophorolipid dimers may be prepared from microbial cultures using yeast.Suitable yeast strains may be selected from, for example, the followinggenera: Candida, Starmerella, Rhodotorula, and Wickerhamiella. Specificstrains suitable for sophorolipid production include, for example, C.bombicola (e.g., ATCC 22214, NRRL Y-30816), Starmerella bombicola,Candida apicola, Candida riodocensis, Candida stellata, and Candida sp.NRRL Y-27208. (See Kurtzman et al., FEMS MicrobioL Lett., 311:140-146(2010)).

In some embodiments, the natural sophorolipid mixture is produced by theyeast C. bombicola or Candida apicola. For example, C. bombicola has anactive extracellular lipase system that first cleaves triglycerides fromvegetable oil into free fatty acids, which are readily taken up by theyeast. The fatty acids then undergo hydroxylation at the ultimate orpenultimate carbon through the action of cytochrome P450. Sophorose isthen added onto the hydroxylated fatty acid by the actions of twoglycosyltransferases. (See Fleurackers, Eur. J. Lipid Sci. Technol.,108: 5-12, (2006)). Acetylation and lactonization complete the formationof sophorolipids, which are then secreted by the yeast.

Fermentation procedures for production of sophorolipids are generallyknown to one of skill in the art. Suitable carbon substrates used in thefermentation to produce the natural sophorolipids may includehydrophobic substrates, for example, vegetable oils (e.g., canola, soy,corn, palm, coconut, sunflower seed, cottonseed, or olive oils), fattyacids (e.g., palmitic, oleic, elaidic, linoleic, alpha-linolenic, orstearic acids), fatty acid esters (e.g., fatty acid methyl ester orfatty acid ethyl ester), alkanes (e.g., pentadecane, hexadecane,heptadecane, or octadecane), and fatty alcohols (e.g., pentadecanol,hexadecanol, heptadecanol, or octadecanol).

The length of the carbon substrates used in the fermentation to producethe natural sophorolipids generally depend on the fermentation host. Forexample, in certain embodiments where a Candida host (e.g., C.bombicola) is used, the fatty acids and/or alkanes have a chain lengthof between fifteen and eighteen carbon atoms. In one variation, fattyacids with carbon chains of between fifteen and eighteen carbon atomsmay be preferable to alkanes with carbon chains of between fifteen andeighteen carbon atoms. (See Van Bogaert et al., Process Biochem., 46(4):821-833 (2011)). In one embodiment, the carbon substrate used in thefermentation to produce the natural sophorolipids is canola oil, whichhas a high C₁₈ content and a monounsaturated fatty acid chain. Further,it should also be understood that other longer or shorter carbonsubstrates can be used, but can be reduced or elongated to between 15and 18 carbon-member chains for use with a Candida host.

Yeast typically produces a mixture of sophorolipids, and thesophorolipid molecules of the mixture usually have one sophorosemolecule linked to a hydroxylated fatty acid at the C-1′ position of thesophorose molecule. The natural sophorolipid mixture may includediacetylated sophorolipids in either lactonic or acidic forms. Fornatural sophorolipid mixtures produced by C. bombicola, diacetylatedlactonic sophorolipids are typically present in a greater amount (e.g.,greater than 60%) than acidic sophorolipids (e.g., less than 10%). SeeAsmer et al., J. Am. Oil Chem. Soc., 65(9):1460-1466 (1988); Davila etal., J. Chromatography, 648:139-149 (1993); Davila et al., J. Indust.Microbio., 13: 249-257 (1994); Ratsep & Shah, J. Microbio. Methods,78:54-356 (2009). The sophorolipids of the natural sophorolipid mixturetypically have acetyl groups at the C-6″ and/or C-6′ positions of thesophorose molecule. See Van Bogaert et al., Process Biochemistry46(4):821-833 (2011). The fatty acid groups may be saturated orunsaturated, and may vary in length. Typically, sophorolipids in anatural sophorolipid mixture have a fatty acid chain of sixteen toeighteen carbon atoms.

The composition of the natural sophorolipid mixture may depend on thetype of feedstock and culture conditions. For example, if the feedstockis a fatty acid ester rather than vegetable oil or free fatty acids,more of the free acidic sophorolipids may be produced. (See Ashby etal., U.S. Published Patent Application No. 2006/0199244.) On the otherhand, if an alkane such as hexadecane or heptadecane is used, more ofthe lactonic sophorolipids are produced. (See Glenns and Cooper, J. Am.Oil Chemist Soc., 83(2):137-145 (2006).)

The following examples are intended only to further illustrate theinvention and are not intended to limit the scope of the invention asdefined by the claims.

EXAMPLES Example 1. Enzymatically Prepared Lactose Acetate Ester forInducing Gene Expression in Trichoderma

This example describes the preparation of the lactose acetate estersdepicted in FIG. 1A from lactose using enzyme-catalyzedtrans-esterification, which enhances their protein induction power inTrichoderma.

The preparation starts first with dissolving 25 mg of D-lactose(Sigma-Aldrich) with 0.20 mL of dimethyl sulfoxide (DMSO) in a 20 mLglass scintillation vial. This was followed with the addition of 1.8 mLof tert-amyl alcohol, 0.125 g of molecular sieve (SYLOSIV, WR Grace,Columbia, Md.), and 0.125 g of immobilized lipase enzyme (Lipozyme TL,Novozymes, Franklinton, N.C.). The mixture was pre-incubated inside ashaker incubator at 50° C. and 150 RPM for 1 hour after which 0.142 mLvinyl acetate (Sigma-Aldrich, St. Louis, Mo.) was added to initiate thetrans-esterification reaction. The reaction was allowed to progress for16 hours inside the shaker incubator at 50° C. and 150 RPM.

At the end of the reaction, the crude product mixture was removed fromthe scintillation vial and recovered as the supernatant viacentrifugation where the solvents were evaporated using a SpeedVacconcentrator (Savant, Thermo Scientific). For NMR and induction studies,the lactose monoacetate was fractionated from the crude mixture by flashchromatography. A 5 g self-packed silica gel (Fisher, 230-400Mesh)column was used with an eluent (1-propanol:ethyl acetate:water, 4:5:1)with isocratic elution.

The purity of the lactose monoacetate ester was confirmed via LC-MSusing a Waters 2695 HPLC with Waters ZQ 2000 Mass spectrometer and aWaters 2487 UV detector. The analysis was conducted using a WatersSymmetry C18 column (4.6×250 mm, 5 μm) with a (5%/95%) acetonitrile andwater eluent containing 0.1% formic acid as the mobile phase runisocratically for a total run time of 15 minutes.

To prepare for protein induction studies using Trichoderma, a citrateminimal media was first prepared. The media composition, as modifiedfrom England et al. (U.S. Pat. No. 7,713,725), consists of 14.4 g/Lcitric acid, 4 g/L KH₂PO₄, 6.35 g/L (NH4)₂SO₄, 2 g/L MgSO₄-7H₂O, 0.53g/L CaCl₂-2H₂O, and trace metal elements at 1 mL/L comprising 5 g/LFeSO₄-7H₂O, 1.6 g/L MnSO₄—H₂O, and 1.4 g/L ZnSO₄-7H₂O. The final pH wasadjusted to 5.50 using NaOH. T. reesei Rut-C30, a cellulasehyper-secretor, was selected as the host to test for protein expression.It was obtained from ATCC (56765) and developed as a catabolicde-repressed strain from classic mutagenesis of parent strain NG14 andthe wild type QM6A (Seidl et al., BMC Genomics, 9:327, (2008)). Topropagate Trichoderma, the freeze-dried stock from ATCC was firstdissolved in sterile deionized water and then transferred onto a PDA(potato dextrose agar) plate (Teknova P0047) using a sterile loop. ThePDA plate was maintained at room temperature under white fluorescentlight and after approximately 7 days, green Trichoderma spores could beseen. In addition, 60% (w/v) glucose stock was prepared and used both ascontrol and as the carbon source for Trichoderma growth.

To initiate protein induction studies, 0.5 mL of glucose stock was firstplaced into 14 mL of citrate minimal media inside a 125 mL baffledflask, followed by the addition of 0.5 mL of prospective inducer. Forthe glucose (no inducer) control, 0.5 mL of glucose stock was placedinto 14.5 mL minimal media to give a final glucose concentration of 2%.To commence the fermentation, an approximately 1 cm by 1 cm square agarplug was removed from the Trichoderma spore-containing PDA agar plateusing a sterile loop and placed into the protein induction culture mediato be tested. The cultures were placed inside a 28° C. incubator withshaking at 175 RPM. At day 3 of fermentation, the samples were collectedand analyzed for CMC (carboxymethylcellulose) endo-glucanase activity.Since the T. reesei Rut-C30 is a cellulase hyper-producer, the CMCactivity directly correlates with the amount of protein being induced.The CMC activity assay follows a procedure modified from Mandels andReese with a 0.3 mL reaction volume (J. Bacteriol., 73:269-278, (1957)).One CMC unit denotes the activity that liberates 1 μmol of reducingsugars (expressed as glucose equivalents) in one minute under specifiedconditions of 50° C. and pH 4.8.

The results for CMC activity assays are given in Table 1, which showsthe cellulase activity of known inducers versus the enzymaticallyprepared crude lactose acetate ester mixture and purified lactosemonoacetate. The crude lactose monoacetate mixture, containing bothlactose monoacetate and lactose diacetate, is already very powerful andhighly efficient. At 0.8 g/L, it easily surpasses the induction power oflactose and cellobiose at 1.0 g/L. Its specific induction power(expressed as units U/mg inducer) is 14 times higher than unmodifiedlactose.

TABLE 1 Inducer concentration Cellulase activity mg/15 U/mL U/mgInduction media* mL mM at day 3 at day 3 glucose control (2%) 0 0 0.28 ±0.17 NA lactose (1.0 g/L) 15 2.92 0.64 0.64 cellobiose (1.0 g/L) 15 2.920.34 0.34 sophorose (0.13 g/L) 2.0 0.38 3.58 26.9 sophorose (1.3 g/L) 203.90 15.0 11.2 Crude lactose acetate mixture 12 NA 7.07 8.84 (0.80 g/L)Purified lactose monoacetate 1.4 0.23 2.05 22.0 (0.09 g/L) Purifiedlactose monoacetate 7.6 1.32 10.1 19.9 (0.51 g/L) Purified lactosemonoacetate 15.8 2.73 14.0 13.3 (1.05 g/L) *All media contain 2% glucoseas carbon source.

Even though the impure crude lactose ester mixture is highly inductive,an equivalent mass of the purified lactose monoacetate is even morepowerful. The specific induction activity of lactose monoacetate at 0.09g/L, 0.51 g/L, and 1.05 g/L, measured at day 3, is approximately 34, 31,and 21 times that of unmodified lactose, respectively. Furthermore, thespecific induction power of the lactose monoacetate at 0.09 g/L (22.0U/mg) nearly approaches that of sophorose (26.9 U/mg), which iscurrently the gold standard for cellulase induction in Trichoderma.

The purified lactose monoacetate was confirmed by LC-MS to contain amolar mass of 384 (402 [M+NH₄]⁺ and 407 [M+Na]⁺). The structure of thelactose monoacetate was further confirmed by analysis using nuclearmagnetic resonance (NMR; Varian 400 mHz).

Based on the spectra of ¹H NMR, ¹³C-NMR, and two dimensional ¹³C-¹H HSQCNMR, the lactose monoacetate as depicted in FIG. 1A was confirmed to bean α and β anomer mixture of lactose monoacetylated at 6″ position. Theassignments of protons and carbons for the isolated lactose monoacetatefraction are summarized in Table 2 below.

TABLE 2 Functional ¹³C-NMR ¹H-NMR groups δ(ppm) δ(ppm) Lactose 1′ α:92.57 α: 4.89 β: 97.21 β: 4.32 2′ α: 72.68 α: 3.17 β: 75.07 β: 2.96 3′α: 71.83 α: 3.59 β: 75.19 β: 3.30 4′ α: 81.89 3.27 β: 81.44 5′ α: 70.23α: 3.70 β: 75.38 β: 3.30 6′ α: 61.05 3.63, 3.72 β: 61.10 1″ α: 104.174.26 β: 104.09 2″ α: 70.86 3.34 β: 70.80 3″ α: 73.38 3.36 β: 73.41 4″68.83 3.62 5″ 72.90 3.74 6″ 64.04 4.08, 4.18 Acetyl group —C═O 170.91 CH₃ 21.28 2.02

Example 2. Enzymatically Prepared Sophorose Acetate Ester for InducingGene Expression in Trichoderma

This example shows that sophorose acetate esters can be prepared fromsophorose through enzyme-catalyzed trans-esterification, which enhancesits protein induction power in Trichoderma. The preparation of crudesophorose ester mixture, purified sophorose diacetate, and thesubsequent induction study followed the procedure described in Example 1except the amount of vinyl acetate used was 0.026 mL.

The CMC activity results shown in Table 3 compare the protein inductionpower of the crude sophorose acetate ester mixture and purifiedsophorose diacetate ester to that of sophorose. The crude mixture eventhough impure is already highly efficient and powerful and at 0.17 g/L.Its specific induction power at 70.2 U/mg is ˜3 times that of unmodifiedsophorose. The purified sophorose diacetate ester is even more powerfuland at 0.12 g/L. Its specific induction power at 193.3 U/mg is ˜7 timesthat of unmodified sophorose.

TABLE 3 Inducer concentration Cellulase activity mg/15 U/mL U/mgInduction media* mL mM at day 3 at day 3 glucose control (2%) 0 0 0.28 ±0.17 NA sophorose (0.13 g/L) 2.0 0.38 3.58 26.9 sophorose (1.3 g/L) 203.90 15.0 11.2 Crude sophorose acetate 2.5 NA 11.7 70.2 mixture (0.17g/L) Purified sophorose 1.8 0.28 23.2 193.3 diacetate (0.12 g/L) *Allmedia contain 2% glucose as carbon source.

The crude sophorose acetate mixture was analyzed by LC-MS using the sameprocedure described in Example 1 and was found to consist of a mixtureof sophorose monoacetate with a mass of 384 (402 [M+NH₄]⁺), diacetatewith a mass of 426 (444 [M+NH₄]⁺), and unreacted sophorose. From theLC-MS, the purity of purified sophorose diacetate ester was confirmed.

Example 3. Enzymatically Prepared Sophorose Palmitate Ester for InducingGene Expression in Trichoderma

This example shows that sophorose palmitate belonging to the structureclass with formula (II) can be prepared from sophorose throughenzyme-catalyzed trans-esterification to further enhance its proteininduction power in Trichoderma.

The preparation of crude sophorose palmitate ester mixture and thesubsequent induction study followed the procedure described in Example 1except that 5 mg of sophorose was used as the substrate and vinylpalmitate (TCI America, Portland, Oreg.) was used instead of vinylacetate. Further purification of the crude product mixture was notcarried out.

The CMC activity results shown in Table 4 compare the protein inductionpower of the crude sophorose palmitate mixture to that of sophorose. Thecrude mixture, even though impure, is already highly efficient andpowerful at 0.17 g/L. Its specific induction power at 73.8 U/mg issimilar to the crude sophorose acetate mixture (Table 3) and is ˜3 timesthat of unmodified sophorose.

TABLE 4 Inducer concentration Cellulase activity mg/15 U/mL U/mgInduction media* mL mM at day 3 at day 3 glucose control (2%) 0 0 0.28 ±0.17 NA sophorose (0.13 g/L) 2.0 0.38 3.58 26.9 sophorose (1.3 g/L) 203.90 15.0 11.2 Crude sophorose palmitate 2.5 NA 12.3 73.8 mixture (0.17g/L) *All media contain 2% glucose as carbon source.

The crude sophorose monopalmitate mixture was analyzed by LC-MS usingthe same procedure described in Example 1 except a mobile phase of(70%/30%) acetonitrile and water containing 0.1% formic acid was usedand the purification was run isocratically for a total run time of 30minutes. The sample was found to consist of a mixture of monopalmitateswith a molar mass of 580 (603 [M+Na]⁺) and dipalmitates with a mass of818 (841 [M+Na]⁺).

Example 4. Chemically Prepared Lactose Acetate Ester for Inducing GeneExpression in Trichoderma

This example shows that lactose acetate ester can be also prepared fromlactose through chemically-catalyzed trans-esterification to enhance itsprotein induction power in Trichoderma.

The procedure starts first with preparing a 0.4 M lactose solution indimethyl sulfoxide (DMSO). The solution (2 mL) was mixed with 3 mg ofpotassium carbonate (K₂CO₃) catalyst and preheated at 50° C. for 30minutes to activate the catalyst. After removing undissolved catalyst,the reaction was initiated by adding vinyl acetate with differing molarratios (vinyl acetate: lactose) in order to control the degree ofsubstitution. Each reaction had a volume of 200 μL and was heated to 60°C. for 30 minutes using a thermocycler without stirring. The subsequentsample recovery and induction study followed the procedure described inExample 1.

The results for CMC activity assays are given in Table 5. The crudelactose acetate ester mixture prepared at a vinyl acetate to lactoseratio of 2:1 gave highest induction. It is very powerful and highlyefficient compared to cellobiose and lactose. At 0.91 g/L, it easilysurpasses the induction power of lactose and cellobiose at 1.0 g/L. Itsspecific induction power (expressed as units U/mg inducer) is 13 timeshigher than unmodified lactose and similar to the enzymatically preparedcrude lactose acetate mixture (Table 1).

TABLE 5 Inducer concentration Cellulase activity mg/15 U/mL U/mgInduction media* mL mM at day 3 at day 3 glucose control (2%) 0 0 0.28 ±0.17 NA lactose (1.0 g/L) 15 2.92 0.64 0.64 cellobiose (1.0 g/L) 15 2.920.34 0.34 sophorose (0.13 g/L) 2.0 0.38 3.58 26.9 sophorose (1.3 g/L) 203.90 15.0 11.2 Crude lactose acetate 13.6 NA 5.66 6.24 mixture (0.91g/L) (Vinyl acetate:Lactose 4:1) Crude lactose acetate 13.6 NA 7.37 8.13mixture (0.91 g/L) (Vinyl acetate:Lactose 2:1) Crude lactose acetate13.6 NA 6.58 7.26 mixture (0.91 g/L) (Vinyl acetate:Lactose 1:1) Crudelactose acetate 13.6 NA 6.21 6.85 mixture (0.91 g/L) (Vinylacetate:Lactose 1:2) Crude lactose acetate 13.6 NA 3.89 4.29 mixture(0.91 g/L) (Vinyl acetate:Lactose 1:4) *All media contain 2% glucose ascarbon source.

Based on LC-MS analysis, the crude lactose acetate mixture, preparedchemically with a varying vinyl acetate to lactose ratio, consists of amixture of acetates with multiple degree of substitution. At high vinylacetate to lactose ratio (e.g. 4:1), majority are triacetates anddiacetates while at lower ratio (e.g. 1:4), majority are monoacetatesand unmodified lactose. A ratio of 2:1 gave the highest induction,yielding a product consisting of mainly mono, di, and triacetate esters.

Example 5. Chemically Prepared Sophorose Acetate Ester for Inducing GeneExpression in Trichoderma

This example shows that sophorose acetate esters can be also preparedfrom sophorose through chemically-catalyzed trans-esterification and howthey can be further purified to enhance their protein induction power inTrichoderma. The procedure of preparing sophorose acetate esterschemically follows the same procedure described in Example 4 andsubsequent sample recovery and induction study followed the proceduredetailed in Example 1 except the crude mixture was further purifiedbased on procedure described in Example 1 to isolate the sophorosediacetate ester.

The results for CMC activity assays are shown in Table 6. The crudesophorose acetate ester mixture, prepared at a vinyl acetate tosophorose ratio of 1:1, gave highest induction. It is very powerful andhighly efficient and greatly exceeds the unmodified sophorose. At 0.09g/L, its specific induction power (expressed as units U/mg inducer) is 5times higher than unmodified sophorose and the crude mixture is furtherpurified to isolated sophorose diacetate ester and its specificinduction is ˜8 times higher than unmodified sophorose.

TABLE 6 Inducer concentration Cellulase activity mg/15 U/mL U/mgInduction media* mL mM at day 3 at day 3 glucose control (2%) 0 0 0.28 ±0.17 NA sophorose (0.13 g/L) 2.0 0.38 3.58 26.9 sophorose (1.3 g/L) 203.90 15.0 11.2 Crude sophorose acetate 2 NA 15.4 115.5 mixture (0.13g/L) (Vinyl acetate:Sophorose 4:1) Crude sophorose acetate 2 NA 17.7132.8 mixture (0.13 g/L) (Vinyl acetate:Sophorose 2:1) Crude sophoroseacetate 2 NA 18.1 135.8 mixture (0.13 g/L) (Vinyl acetate:Sophorose 1:1)Crude sophorose acetate 1.37 NA 13.4 147.0 mixture (0.09 g/L) (Vinylacetate:Sophorose 1:1) Crude sophorose acetate 1.37 NA 9.45 103.5mixture (0.09 g/L) (Vinyl acetate:Sophorose 1:2) Crude sophorose acetate1.37 NA 7.68 84.1 mixture (0.09 g/L) (Vinyl acetate:Sophorose 1:4)Purified sophorose diacetate 0.45 0.07 6.33 211.0 (0.03 g/L) *All mediacontain 2% glucose as carbon source.

Based on LC-MS analysis, the crude sophorose acetate mixture, preparedchemically with a varying vinyl acetate to sophorose ratio, consists ofa mixture of acetates with multiple degree of substitution. At highvinyl acetate to sophorose ratio (e.g. 4:1), the products are mainlytri-, tetra-, penta-, and hexa-acetates, while at lower ratio (e.g.1:4), the products are mainly are di- and mono-acetates and unmodifiedsophorose. The ratio of 1:1 gave the highest induction, and the majorityof the products are mono-, di-, and tri-acetate esters.

The purified sophorose diacetate ester was confirmed by LC-MS to containa molar mass of 426 (444 [M+NH4]+ and 449 [M+Na]+). The structure of thesophorose diacetate was further confirmed by analysis using nuclearmagnetic resonance (NMR; Varian 400 mHz).

Based on the spectra of ¹H NMR, ¹³C-NMR, and two dimensional ¹³C-¹H HSQCNMR, the sophorose diacetate as depicted by FIG. 1B was confirmed to bean alpha-sophorose diester acetylated at both 6′ and 6″ position. Theassignments of protons and carbons for the isolated sophorose acetatefraction are summarized in Table 7 below.

TABLE 7 Functional ¹³C-NMR ¹H-NMR groups δ(ppm) δ(ppm) Sophorose 1′ 91.65.06 1″ 105.1  4.32 2′ 82.1 3.19 2″ 73.7 3.06 3′ 71.3 3.64 3″ 76.0 3.144′ 70.0 3.16 4″ 70.1 3.11 5′ 68.9 3.77 5″ 73.4 3.36 6′ a, 6″ a 63.6,63.9 4.02 6′ b, 6″ b 4.23 Acetyl group —C═O 170.3  CH₃ (6′) 20.7 2.00CH₃ (6″) 20.7 2.01

Example 6. Chemically Prepared Maltose Acetate Ester for Inducing GeneExpression in Aspergillus

This example shows that maltose acetate ester can be also prepared frommaltose through chemically-catalyzed trans-esterification to enhance itsprotein induction power in Aspergillus. The procedure of preparingmaltose acetate chemically and subsequent sample recovery follows thesame procedure described in Example 4. To prepare for protein inductionstudies using Aspergillus, a minimum media was first prepared with 1 g/LKH₂PO₄, 2 g/L NH₄Cl, 0.5 g/L MgSO₄-7H₂O, 0.2 mg/L CuSO₄-5H₂O, 12.5 mg/LFeSO₄-7H₂O, 1 mg/L ZnSO₄-7H₂O, and 0.09 mg/L MnSO₄ . Aspergillus niger(NRRL 330), obtained from ARS culture collection, was maintained on aPDA plate and allowed to sporulate for a week at room temperature. Forinoculation, a 2 cm by 2 cm area agar plug was first removed andsuspended in 5 mL sterile water. The spores were washed off from agarwith vigorous agitation and 1 mL of the suspension was used as inoculumwith 14 mL media and 1% sorbitol as carbon source in a 125 mL baffledflask. The cultures were allowed to progress inside a shaker incubator(28° C. and 200 RPM) for 2 days at which time the inducer was added.After additional 24 hours, the cultures were assayed for amylaseactivity following similar procedures to those detailed by Barton et al.(J. Bacteriol., 1972, 111 (3):771-777).

The results for amylase activity assays are shown in Table 8. The crudemaltose acetate ester mixture prepared at a vinyl acetate to maltoseratio of 2:1 gave highest induction. It is more powerful and highlyefficient compared to maltose. At 0.05 g/L, its specific induction power(138.1 U/mg) is 3 times higher than unmodified maltose (44.0 U/mg).

TABLE 8 Inducer concentration Amylase activity mg/15 U/mL U/mg Inductionmedia* mL mM at day 3 at day 3 Maltose control (0.05 g/L) 0.72 0.14 2.1144.0 Crude maltose acetate 0.72 NA 3.64 75.8 mixture (0.05 g/L) (Vinylacetate:maltose 4:1) Crude maltose acetate 0.72 NA 6.63 138.1 mixture(0.05 g/L) (Vinyl acetate:maltose 2:1) Crude maltose acetate 0.72 NA6.03 125.6 mixture (0.05 g/L) (Vinyl acetate:maltose 1:1) Crude maltoseacetate 0.72 NA 5.66 117.9 mixture (0.05 g/L) (Vinyl acetate:maltose1:2) *All media contain 1% sorbitol as carbon source.

Based on LC-MS analysis, the crude maltose acetate mixture, preparedchemically with a varying vinyl acetate to maltose ratio, consists of amixture of acetates with multiple degree of substitutions. At high vinylacetate to maltose ratio (e.g. 4:1), the product is mainly tri-, tetra-,penta-, and hexa-acetates, while at a lower ratio (e.g. 1:2), theproduct is mainly tri-, di-, and mono-acetates and unmodified maltose.The ratio of 2:1 gave the highest induction, and the product is mainlymono-, di-, and tri-acetate esters.

Example 7. Sophorose Esters Obtained from Formic Acid Treatment ofNatural Lactonic Sophorolipid for Inducing Gene Expression inTrichoderma

This example describes a highly effective method of using formic acid toconvert non-inductive natural lactonic sophorolipid into novel andhighly inductive sophorose esters with structures described by FIG. 1Dand FIG. 2. To prepare natural lactonic sophorolipid, C. bombicola (ATCC22214) was used. A sample of freeze-dried stock in a glass vial wasobtained from ATCC and was first transferred into a yeast extract,peptone, dextrose (YPD) culture broth, then allowed to grow for 48 hoursat 28° C. for two days. The culture was then mixed with sterilizedglycerol to prepare a final culture containing 20% glycerol. A cell bankwas then established using cryovials with 1 mL of seed culture each, andstored at −80° C.

For the production of natural sophorolipids from canola oil, aproduction medium was first prepared and included the followingcomponents: 100 g/L glucose, 10 g/L yeast extract, 1 g/L urea, and 100g/L canola oil (Crisco, The J.M. Smucker Company, Orrville, Ohio). Basedon the data provided from the manufacturer, the canola oil has 64%monounsaturated fat from mainly oleic fatty acid, and 29%polyunsaturated fat from mainly linoleic and alpha-linolenic fattyacids. To initiate the fermentation, a 1 mL seed of C. bombicola from acryovial as prepared above was placed into 50 mL of production mediuminside a 250 mL baffled flask incubated at 28° C. and 250 revolutionsper minute (RPM). After seven days, sophorolipids appeared in the mediaas a viscous brown oily phase, and in some cases, the sophorolipidcrystallized into a yellow to white colored residue. The brown oilysophorolipid was isolated using a separation funnel and further purifiedto recover diacetylated lactonic sophorolipids using a self-packedsilica gel column (Fisher, 230-400 Mesh) eluted isocractically usingethyl acetate. To recover crystalline sophorolipids consisting of mostlydiacetylated lactonic sophorolipid, sophorolipids were allowed to standuntil sediment formed, which was recovered by decanting and washing withwater followed by freeze drying. The purity of harvested samples wasconfirmed by the result from LC-MS and found be a diacetylated lactonicsophorolipid derivatized with hydroxy oleate fatty groups with a molarmass of 688 (706 [M+H₂NH₄]⁺ and 711 [M+Na]⁺).

The next step was treatment with formic acid. The process began bydissolving 5 mg diacetylated lactonic sophorolipid in 200 μL formicacid. In certain runs, this step was followed by addition of 0.31 μL(0.15%) of concentrated sulfuric acid. The reaction mixture was heatedto 80° C. in a thermocycler for 30 minutes without stirring. Water (1mL) was then added to precipitate the sample, followed by centrifugationto recover the precipitate and drying in a SpeedVac to remove residualwater and formic acid. The dried sample was then solublized in 200 μLacetic acid to methanol (3:2 v/v) solution and heated to 90° C. for 6hours to cleave unwanted formate ester from the treated sophorolipid.This step was followed with another drying step using a SpeedVac toremove acetic acid and methanol. The final samples, which were a crudemixture of products, were tested for induction in Trichoderma followingthe procedure described in Example 1.

The CMC activity results shown in Table 9 compare the protein inductionpower of the crude sophorose ester obtained from the formic acidtreatment of natural lactonic sophorolipid to other known inducers. Thetested samples, even though impure, were highly efficient and powerfulcompared to known inducers. The natural diacetylated lactonicsophorolipid is not inductive relative to the glucose control and, afterformic acid treatment, its specific induction at 0.33 g/L is enhanced52-fold. If 0.15% sulfuric acid is used together with formic acid, thespecific induction is enhanced by as much as 487-fold at a concentrationof 0.03 g/L. Even as an impure, crude sample, the specific inductionpower of the mixture at 496.5 U/mg is 18 times that of sophorose, thecurrent best in class inducer.

TABLE 9 Inducer concentration Cellulase activity mg/15 U/mL U/mgInduction media* mL mM at day 3 at day 3 glucose control (2%) 0 0 0.28 ±0.17 NA lactose (1.0 g/L) 15 2.92 0.64 0.64 cellobiose (1.0 g/L) 15 2.920.34 0.34 sophorose (0.13 g/L) 2.0 0.38 3.58 26.9 sophorose (1.3 g/L) 203.90 15.0 11.2 Untreated diacetylated 5 0.48 0.34 1.02 lactonicsophorolipid (0.33 g/L) Formic acid treatment 5 NA 17.7 53.1 (0.33 g/L)Formic acid + 0.15% 5 NA 29.5 88.5 sulfuric acid treatment (0.33 g/L)Formic acid + 0.15% 2.5 NA 29.3 175.8 sulfuric acid treatment (0.17 g/L)Formic acid + 0.15% 1 NA 22.7 340.5 sulfuric acid treatment (0.07 g/L)Formic acid + 0.15% 0.5 NA 16.6 496.5 sulfuric acid treatment (0.03 g/L)*All media contain 2% glucose as carbon source.

Example 8. Natural Sophorolipid Dimer Esters Obtained from C. bombicolaCulture for Inducing Gene Expression in Trichoderma

This example illustrates that the natural sophorolipid dimer depicted inFIG. 1E, can also serve as a highly efficient inducer for geneexpression in Trichoderma. A crude sample containing the sophorolipiddimer was prepared from the cultures of C. bombicola according theprocedures described in Example 7 and was typically harvested as a brownoily residue. In addition to canola oil, soybean and corn oil were alsoused as feedstock (Crisco, The J.M. Smucker Company, Orrville, Ohio). Inmost cases, the C. bombicola yeast did not produce the dimericsophorolipid. In a few cases, a trace amount was produced and itspresence was revealed by LC-MS, which showed molar masses of 1030, 1028,1072, 1070, 1114, and 1112 (1053[M+Na]⁺, 1051[M+Na]⁺, 1095[M+Na]⁺,1093[M+Na]⁺, 1137[M+Na]⁺, and 1135[M+Na]⁺, respectively). The molarmasses 1030 and 1028 denote a diacetylated sophorolipid dimerderivatized with an oleate or a linoleate fatty group, respectively. Themolar masses 1072 and 1070 denote a triacetylated dimer derivatized withan oleate or a linoleate fatty group, respectively. The molar masses of1114 and 1112 denote a tetra-acetylated dimer derivatized with an oleateor a linoleate fatty group, respectively. These dimeric compounds werenot further isolated, and induction studies were carried out using crudesamples following the procedures described in Example 1.

The CMC activity results shown in Table 10 compare the protein inductionpower of the crude sophorolipid dimer mixture obtained from C. bombicolaculture to other known inducers. The crude samples, even though impureas shown by LC-MS and TLC, are highly efficient and powerful comparingto known inducers. The crude sample that does not contain dimers issignificantly less inductive than samples containing dimers. At 0.90g/L, the specific induction (19.7 U/mg) of the sample containing dimergrown on canola oil is 7 times the induction produced by the samplewithout dimer and nearly approaches that of sophorose (26.9 U/mg). Sincethese dimers exist as only trace amounts in the crude sample, purifieddimeric compounds once isolated may be even more powerful.

TABLE 10 Inducer concentration Cellulase activity mg/15 U/mL U/mgInduction media* mL mM at day 3 at day 3 glucose control (2%) 0 0 0.28 ±0.17 NA lactose (1.0 g/L) 15 2.92 0.64 0.64 cellobiose (1.0 g/L) 15 2.920.34 0.34 sophorose (0.13 g/L) 2.0 0.38 3.58 26.9 sophorose (1.3 g/L) 203.90 15.0 11.2 Crude sample without 16 NA 2.90 2.72 dimers grown oncanola oil (1.07 g/L) Crude sample containing 12.5 NA 16.4 19.7 dimersgrown on canola oil (0.90 g/L) Crude sample containing 12.5 NA 14.5 17.4dimers grown on soybean oil (0.90 g/L) Crude sample containing 12.5 NA15.5 18.6 dimers grown on corn oil (0.90 g/L) *All media contain 2%glucose as carbon source.

Example 9. Sophorose Production from Natural Sophorosides Using FormicAcid

In order to be most useful in commercial applications, sophorose needsto become cheaper and more readily available. This example provides asimple and effective method to produce sophorose in high yield fromformic acid treatment of natural sophoroside (stevioside andsophorolipid) under non-aqueous conditions. The procedure is similar tothat described in Example 7, except that the samples were freeze driedafter formic acid treatment and then solublized in 0.5 M sodiummethoxide in methanol for 15 minutes at room temperature. This processremoves unwanted formate or fatty esters to produce sophorose. Afteranother drying step using a SpeedVac to remove methanol, the sample wasanalyzed by HPLC (Waters 2695, 401 RI detector, and BioRad HPX-87Hcolumn) to determine the sophorose concentration. As a comparison,stevioside was treated with 0.1 N hydrochloric acid to yield sophorosefollowing the procedure detailed by Kusakabe et al. (Agric. Biol. Chem.,1987, 51 (8):2255-2256).

The results in Table 11 show that when compared with the dilutehydrochloric acid treatment described by Kusakabe, the formic acidtreatment produces a significantly increased yield. Using stevioside asa starting material, the yield of sophorose tripled using the formicacid treatment. Using diacetylated lactonic sophorolipid as a startingmaterial, the yield of sophorose was doubled when the formic acidtreatment was supplemented with addition of 0.15% sulfuric acid.

TABLE 11 Theo- Recov- retical erable Sophoroside Treatment sophorosesophorose Yield 5 mg stevioside 0.1N HCl, 100° C., 1.91 mg 0.353 mg18.5% 2 hr 5 mg stevioside Formic acid, 80° C., 1.91 mg  1.08 mg 56.5%30 min 5 mg stevioside Formic acid + 1.91 mg  1.07 mg 56.0% 0.15%sulfuric acid, 80° C., 30 min 5 mg diacetylated Formic acid, 80° C., 2.4 mg 0.449 mg 20.0% lactonic 30 min sophorolipid 5 mg diacetylatedFormic acid +  2.4 mg 0.861 mg 38.4% lactonic 0.15% sulfuric acid,sophorolipid 80° C., 30 min

Example 10. Use of Sophorose Ester as Inducer for Gene Expression inSolid Phase Fermentation

Production of enzymes and other protein products using solid phasefermentation relies on the growth of microbes (in particular,filamentous fungi) on moist solid substrates without free-flowingliquid. In contrast to liquid-submerged fermentation, solid phasefermentation in some situations can offer significant advantages in bothperformance and production cost. This example demonstrates thatsophorose ester with structures described by FIG. 1D and FIG. 2 can beused as a very effective inducer for cellulase production in solid phasefermentation using T. reesei.

The solid substrate used was a 1:1 blend of wheat bran and corn cobpurchased from local pet supply store. Each run consisted of 8 grams ofthis blend placed into a 125 mL flask, which was then sterilized byautoclaving. The citrate minimum media (pH 4.8) described in Example 1was then added. The amounts of citrate media added were 5.3 mL, 8 mL, 12mL, 18.7 mL, which gave a starting moisture content of 40%, 50%, 60%,and 70%, respectively. The sophorose ester used was a crude mixtureobtained from the formic acid treatment of the natural lactonicsophorolipid (Example 7). For each run, crude sophorose ester (10 mg)premixed with citrate minimum media was then mixed into the solidsubstrate. Fermentation was initiated by mixing a 2 mL inoculum of T.reesei preculture (from day 2, Example 1) into the solid substratefollowed by incubating the flasks at 28° C. without shaking. The solidsample from each flask was harvested at day 3 and washed with tenvolumes of 50 mM citrate buffer (pH 4.8) and analyzed for CMC activityas described in Example 1.

The results in Table 12 show that regardless of the starting moisturecontent, the addition of sophorose ester inducer to the solid substratewas able to significantly improve the cellulase production in the solidphase fermentation using T. reesei. At 40%, 50%, 60%, and 70% startingmoisture, the observed improvements in cellulase activity per gram solidsubstrate are 4 fold, 7 fold, 12 fold, and 5 fold, respectively.

TABLE 12 Induction media Cellulase activity at day 3 (wheat bran:corncob, 1:1) (U/g solids) 40% moisture control 7.40 40% moisture + 10 mgsophorose ester 27.6 50% moisture control 3.37 50% moisture + 10 mgsophorose ester 22.2 60% moisture control 1.78 60% moisture + 10 mgsophorose ester 21.6 70% moisture control 5.45 70% moisture + 10 mgsophorose ester 24.6

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. It is intended thatthe following claims define the scope of the invention and that methodsand structures within the scope of these claims and their equivalents becovered thereby.

1.-60. (canceled)
 61. A method for producing a protein of interest,comprising: a) providing a fermentation host; and b) culturing thefermentation host with a carbon source and an inducer compound selectedfrom the group consisting of:

where R_(a) is H or C(O)CH₃; R_(b) is H or C(O)CH₃; R_(c) is H orC(O)CH₃; R_(d) is H or C(O)CH₃; R_(e) is H or C(O)CH₃; R_(f) is H orC(O)CH₃; and R_(g) is H or C(O)CH₃, R is a C1-C24 aliphatic moiety, andwherein the fermentation host is cultured under conditions sufficient toproduce the protein of interest.
 62. The method of claim 61, wherein thecarbon source comprises one or more of glucose, sucrose, fructose,lactose, cellulose, cellulose hydrolysate, starch, starch hydrolysate,maltose, or maltodextrin.
 63. The method of claim 61, wherein theprotein of interest comprises a cellulase or an amylase.
 64. The methodof claim 61, wherein the fermentation host comprises a filamentousfungus of the genus Trichoderma or Aspergillus.
 65. The method of claim64, wherein the fermentation host is Trichoderma reesei, Trichodermaviride, Aspergillus niger, or Aspergillus oryzae.
 66. The method ofclaim 61, wherein the inducer compound is provided in at least traceamounts in an inducer crude mixture.
 67. The method of claim 66, whereinthe inducer crude mixture is added to the culture in an amount of about0.9 grams of inducer crude mixture per liter of culture.
 68. The methodof claim 66, wherein the inducer crude mixture provides a specificinduction of greater than or equal to about 17.4 U/mg at day
 3. 69. Themethod of claim 61, wherein R is selected from the group consisting ofunsubstituted C₁-C₂₄ alkyl; C₁-C₂₄ alkyl substituted with hydroxyl,carboxyl or aromatic groups; unsubstituted C₁-C₂₄ alkenyl; and C₁-C₂₄alkenyl substituted with hydroxyl, carboxyl or aromatic groups.
 70. Themethod of claim 61, wherein R is an aliphatic moiety selected fromunsubstituted C₁-C₂₄ alkyl, substituted C₁-C₂₄ alkyl, unsubstitutedC₁-C₂₄ alkenyl, and substituted C₁-C₂₄ alkenyl.
 71. The method of claim61, wherein R is an aliphatic moiety selected from C₁-C₂₄ alkylsubstituted with hydroxyl groups and C₁-C₂₄ alkenyl substituted withhydroxyl groups.
 72. The method of claim 61, wherein R is an aliphaticmoiety selected from C₁-C₂₄ alkyl substituted with carboxyl groups andC₁-C₂₄ alkenyl substituted with carboxyl groups.
 73. The method of claim61, wherein R is an aliphatic moiety selected from C₁-C₂₄ alkylsubstituted with aromatic groups and C₁-C₂₄ alkenyl substituted witharomatic groups.
 74. A method for producing a protein of interest,comprising: a) providing a fermentation host; and b) culturing thefermentation host with a carbon source and an inducer compound selectedfrom the group consisting of:

where R_(a) is H or C(O)CH₃; R_(b) is H or C(O)CH₃; R_(c) is H orC(O)CH₃; R_(d) is H or C(O)CH₃; R_(e) is H or C(O)CH₃; R_(f) is H orC(O)CH₃; and R_(g) is H or C(O)CH₃, R is a C₁-C₂₄ aliphatic moiety, andwherein the fermentation host is cultured under conditions sufficient toproduce the protein of interest.
 75. The method of claim 74, wherein theprotein of interest comprises a cellulase or an amylase.
 76. The methodof claim 74, wherein the fermentation host comprises a filamentousfungus of the genus Trichoderma or Aspergillus.
 77. The method of claim76, wherein the fermentation host is Trichoderma reesei, Trichodermaviride, Aspergillus niger, or Aspergillus oryzae.
 78. The method ofclaim 74, wherein the inducer compound is provided in at least traceamounts in an inducer crude mixture, and wherein the inducer crudemixture is added to the culture in an amount of about 0.9 grams ofinducer crude mixture per liter of culture.
 79. The method of claim 78,wherein the inducer crude mixture provides a specific induction ofgreater than or equal to about 17.4 U/mg at day
 3. 80. A method forproducing a protein of interest, comprising: a) providing a fermentationhost; and b) culturing the fermentation host with a carbon source, andan inducer compound of formula (II)

where R_(a) is H or C(O)CH₃; R_(b) is H or C(O)CH₃; R_(c) is H orC(O)CH₃; and wherein the fermentation host is cultured under conditionssufficient to produce the protein of interest.